1. Field of Invention
The present invention relates to a projection display device to perform light modulation using a plurality of liquid crystal light valves.
2. Description of Related Art
In recent years, a projection display device capable of providing a color display has been put to practical use. Such a related art projection display device typically includes liquid crystal light valves corresponding to three stimuli of red (R), green (G), and blue (B) display systems. One related art projection display device displays an image by modulating lights of three primary colors (R, G, and B) incident upon the corresponding liquid crystal light valves and superimposing the primary lights modulated by the corresponding liquid crystal light valves upon each other. See, for example, Japanese Unexamined Patent Application Publication No. 63-271232.
In the related art, a liquid crystal material of the liquid crystal light valves is known to decompose and deteriorate easily when it is irradiated with ultraviolet light or near ultraviolet light (blue light having a short wavelength) with high energy. Therefore, ordinarily, for example, ultraviolet (UV) cut filters to protect the liquid crystals from light of wavelengths in the ultraviolet and near ultraviolet wavelength band are disposed between a light source and the liquid crystal light valves in order to reduce or prevent the light from entering the liquid crystal light valves.
In recent years, in order to increase brightness and a color reproduction range, a projection display device is constructed using a high-intensity lamp, such as a metal halide lamp or an extra-high pressure mercury lamp, as a light source. FIG. 9 is a graph showing a spectral distribution of a metal halide lamp that lights up by alternating current. FIG. 10 is a graph showing a spectral distribution of an extra-high pressure mercury lamp that lights up by direct current. As shown in FIGS. 9 and 10, these types of lamps have a very large amount of light components having short wavelengths in the visible range.
Therefore, even if, for example, the aforementioned UV cut filters are used, the liquid crystal light valve to modulate blue light having high intensity and relatively high energy deteriorates considerably more quickly than the liquid crystal light valves to modulate the other primary lights.